Life from outer space could be surviving on the outer fringes of the Earth's atmosphere, according to scientists who are to launch a mission to search for bacteria that could be living there.

In science fiction films the search for aliens involves travelling across the galaxy to planets millions of miles away.

But scientists believe they could be close to discovering alien life forms much closer to home – on the outer fringes of Earth's atmosphere.

British scientists, working with the European Space Agency, will this week launch a balloon carrying instruments to search the stratosphere for bacteria and other microorganisms.

They believe there could be species capable of surviving in the high levels of radiation, extreme cold and near vacuum found on the edge of space.

The organisms could be entirely new to science and may even have been brought here from outer space by hitching a ride on asteroids or comets.

If they succeed, it would be the first time alien life had been captured and would lend substantial weight to theories that all life on Earth was brought here from elsewhere in the galaxy.

They also hope they may find new types of bacteria that have been thrown up into the atmosphere by erupting volcanoes.

Clara Juanes-Vallejo, who is leading the research team at Cranfield University, said: "There are theories that life on Earth came from space, so we need to know that life can survive the conditions of space for this to be true.

"The environment in the stratosphere is very extreme. It can get down to -90 degrees C and is a near vacuum. There is also a lot of harmful radiation as there is not the same level of protection as we get from the atmosphere.

"If we know that life can survive in such an extreme environment, then it could also survive in places like Mars or on asteroids.

"If we find microorganisms up there, there are a number of ways it could have arrived. It could have come from space itself, or it could be from our own volcanoes that have projected material up there."

The €70,000 balloon-borne mission, which has been developed along with electronics firm Alpha Micro, will be sent more than 21 miles into the air above the arctic circle where it will suck the thin air through a series of filters.

These will collect any microorganisms out of the atmosphere before being sealed and returned back to Earth to be analysed.

At that altitude, air pressure is a hundredth of that found on the ground and there are high levels of harmful ultraviolet light, which can kill most forms of life.

But scientists have already found bacteria on Earth which thrives in similar conditions and some species of bacteria can form spores which allows them to survive inhospitable conditions for long periods of time.

Nine years ago scientist from India attempted to discover if life could exist in the stratosphere but their findings were quickly cast into doubt by claims they had failed to ensure the collecting equipment was sterile.

The new mission, called CASS-E has been assembled in a sterile environment normally reserved for missions being sent to other planets such as Mars.

It also has been fitted with special seals to prevent any bacteria from Earth that is being carried on the surface of the instrument getting inside the sterile collection area.

Life is thought to have first emerged on Earth around 3.8 billion years ago but how it started has been a topic of much debate.

Some astrobiologists believe that the seeds for life on Earth actually began elsewhere in the galaxy and microbes were carried here on an icy asteroid or comet that collided with our planet.

Recent research has also suggested that life on Earth could even predate a heavy asteroid bombardment around 3.9 billion years ago by surviving in underground habitats where it was protected from the impacts.

Asteroids still continue to hit the Earth – last year there was an explosion over Indonesia – but are far less regular and most tend to burn up in the atmosphere.

Scientists claim that some could leave life behind in the outer atmosphere before they burn up.